Heat pipe with a tube therein

ABSTRACT

A heat pipe includes a metal casing ( 100 ) filled with a working fluid therein, a capillary wick ( 200 ) provided inside of the metal casing and a tube ( 300 ) contacting with a surface of the capillary wick. The capillary wick extends in an axial direction of the casing and has a middle portion separated from an inner wall of the metal casing. A vapor passage ( 700 ) is formed between an outer wall of the tube and the inner wall of the casing and a liquid channel ( 800 ) is defined by the capillary wick. The working fluid in vapor state flows along the vapor passage and the working fluid in liquid flows along the liquid channel. The tube separates the vapor from the liquid at a place where the tube is located.

DESCRIPTION

1. Field of the Invention

The present invention relates generally to heat pipes as heattransfer/dissipating device, and more particularly to a heat pipe with atube therein.

2. Description of Related Art

Heat pipes have excellent heat properties, and therefore are aneffective means for heat transfer or dissipation from heat sources.Currently, heat pipes are widely used for removing heat fromheat-generating components such as central processing units (CPUs) ofcomputers. FIG. 6 shows an example of a related heat pipe. The heat pipeincludes a vacuum casing 10 containing a working fluid therein (notshown) and a capillary wick 20 attached to an inner surface of thecasing 10. The casing 10 includes an evaporating section 40 at one endand a condensing section 60 at the other end. An adiabatic section 50 isprovided between the evaporating and condensing sections 40, 60. Theadiabatic section 50 is typically used for transport of the generatedvapor from the evaporating section 40 to the condensing section 60. Avapor channel 70 is formed in the central of an inside of the casing 10and a liquid channel 80 is defined by the capillary wick 20. As theevaporating section 40 of the heat pipe is maintained in thermal contactwith a heat-generating component, the working fluid contained in theevaporating section 40 absorbs heat generated by the heat-generatingcomponent and then turns into vapor. Due to the difference of vaporpressure between the evaporating and condensing sections 40, 60 of theheat pipe, the generated vapor moves towards and carries the heatsimultaneously to the condensing section 60 along the vapor channel 70.The vapor is condensed into liquid at the condensing section 60 afterreleasing the heat into ambient environment. FIG. 7 is adiagrammatically longitudinal cross-sectional view showing oppositeflowing paths between vapor and condensed liquid of the working fluid inthe casing 10 of the heat pipe. Because of contacts of the vapor and thecondensed liquid, an entrainment limit caused by the opposite flowingbetween the vapor and the condensed liquid prevents circulations of thevapor and condensed liquid. The condensed liquid is heated before itreaches the evaporating section 40. Accordingly, heat-transferredability of the heat pipe is weakened and heat dissipation efficiency ofthe heat pipe is lowered.

In view of the above-mentioned disadvantage of the conventional heatpipe, there is a need for a heat pipe having a good heat transfereffect.

SUMMARY OF THE INVENTION

A heat pipe in accordance with a preferred embodiment includes a metalcasing containing a working fluid therein and a capillary wick providedin an inside of the casing. The capillary wick extends in an axialdirection of the casing and has a middle portion separated from an innerwall of the metal casing. A tube is provided to contact with a surfaceof the capillary wick to separate the capillary wick from a vaporpassage in the heat pipe.

Other advantages and novel features will become more apparent from thefollowing detailed description of preferred embodiments when taken inconjunction with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present apparatus and method can be betterunderstood with reference to the following drawings. The components inthe drawings are not necessarily drawn to scale, the emphasis insteadbeing placed upon clearly illustrating the principles of the presentapparatus and method. Moreover, in the drawings, like reference numeralsdesignate corresponding parts throughout the several views.

FIG. 1 is a longitudinal cross-sectional view of a heat pipe inaccordance with a first embodiment of the present invention;

FIG. 2 is a radial cross-sectional view of the heat pipe in accordancewith the first embodiment, taken along line II-II of FIG. 1;

FIG. 3 is a longitudinal cross-sectional view of a heat pipe inaccordance with a second embodiment of the present invention;

FIG. 4 is a radial cross-sectional view of a heat pipe in accordancewith a third embodiment of the present invention;

FIG. 5 is a radial cross-sectional view of a heat pipe in accordancewith a fourth embodiment of the present invention;

FIG. 6 is a longitudinal cross-sectional view of a heat pipe inaccordance with related art; and

FIG. 7 is a diagrammatically longitudinal cross-sectional view showingvapor and liquid moving paths of the related heat pipe of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-2 show a heat pipe in accordance with a first embodiment of thepresent invention. The heat pipe comprises a metal casing 100 made ofhigh thermally conductive materials such as copper or copper alloys, aworking fluid (not shown) contained in the casing 100 and a capillarywick 200 arranged inside of the casing 100. The casing 100 comprises anevaporating section 400 at one end, a condensing section 600 at theother end and an adiabatic section 500 arranged between the evaporatingsection 400 and the condensing section 600. The capillary wick 200comprises first capillary wicks 220 disposed in opposite ends of thecasing 100, respectively, and a second capillary wick 240interconnecting with the first capillary wicks 220. The first capillarywicks 220 are arranged on the evaporating and condensing sections 400,600 of the casing 100. The second capillary wick 240 extends in an axialdirection of the casing 100. A tube 300 surrounds the second capillarywick 240 so that an inner surface of the tube 300 is attached with anouter surface of the second capillary wick 240 in the casing 100. Thefirst capillary wicks 220 contact with the casing 100, while the secondcapillary wick is separated from the casing 100. A vapor passage 700 isprovided between the tube 300 and an inner wall of the casing 100 and aliquid channel 800 is defined by the first and second capillary wicks220, 240. The vapor passage 700 is separated from the second capillarywick 240 by the tube 300 at the adiabatic section 500. The tube 300 canreach the evaporating and condensing sections 400, 600 of the casing 100with a proper range.

As the evaporating section 400 of the heat pipe is maintained in thermalcontact with a heat-generating component (not shown), the working fluidcontained in the evaporating section 400 absorbs heat generated by theheat-generating component and then turns into vapor. Due to thedifference of vapor pressure between the evaporating and condensingsections 400, 600 of the heat pipe, the generated vapor moves along thevapor passage 700 and carries the heat simultaneously to the condensingsection 600. The vapor is condensed into liquid at the condensingsection 600 after releasing the heat into ambient environment. Becauseof an arrangement of the tube 300 attached on the second capillary wick240 at the adiabatic section 500, the vapor flows only along the vaporpassage 700 toward the condensing section 600 and the liquid flows onlyin the liquid channel 800 towards the evaporating section 400 when theyflow in the adiabatic section 500. The vapor and the liquid in theadiabatic section 50 are separated by the metal tube 300, which canavoid the adverse contact between the vapor and liquid. Thus, thecondensed working fluid from the condensing section 600 can smoothlyreach the evaporating section 400 and is prevented from being heated bythe high temperature vapor at the adiabatic section 500. Abilities ofheat-absorption and heat-dissipation of the working fluid of the heatpipe is enhanced and heat-transfer efficiency of the heat pipe isaccordingly improved.

FIG. 3 illustrates a heat pipe according to a second embodiment of thepresent invention. Main differences between the second and firstembodiments are that in the second embodiment the capillary wick 200further comprises a third capillary wick 230 attached on the inner wallof the casing 100 at the evaporating section 400. The third capillarywick 230 is a thin layer extending from an end of the first capillarywick 220 at the evaporating section 400 of the casing 100. The thirdcapillary wick 230 is so thin that it can guide the vapor at theevaporating section 400 into the vapor passage 700 quickly. Portions ofthe first capillary wicks 220 near the second capillary wick 240 eachhave a graduated thickness: the thickness at the evaporating section 400is gradually decreased along a direction from the evaporating section400 toward the adiabatic section 500, and at the condensing section 600is gradually increased from the adiabatic section 500 toward thecondensing section 600. The third capillary wick 230 is much thinnerthan that of the first and second capillary wicks 220, 240. As theevaporating section 400 of the heat pipe absorbs the heat generated bythe heat-generating component, the heated working fluid can turn intovapor quickly and then flow into the vapor passage 700 towards thecondensing section 600 of the casing 100. The vapor passage 700 isseparated from the second capillary wick 240 by the tube 300. A liquidchannel 820 is defined by the first, second and third capillary wicks220, 240 and 230. The condensed liquid in the condensing section 600flows along the liquid channel 820 and is drawn back to the evaporatingsection 400 under capillary pressure developed by the first and secondcapillary wicks 220, 240 to achieve a thermal circulation.

FIG. 4 illustrates a heat pipe according to a third embodiment of thepresent invention. Four spaced ribs 310 are disposed between an outerwall of the tube 300 and the inner wall of the casing 100 so as toreinforce the heat pipe. The other structure of the heat pipe of thethird embodiment is similar to that of the first embodiment.

FIG. 5 illustrates a heat pipe according to a fourth embodiment of thepresent invention. Four-spaced small pipes 320 are disposed surroundingthe tube 300 and an inner surface of each small pipe 320 is filled witha supplementary second capillary wick 240. Each small pipe 320 extendsin a longitudinal direction of the casing 100 and is sandwiched betweenan outer wall of the tube 300 and the inner wall of the casing 100. Thevapor passage 700 is enclosed by the inner wall of the casing 100 anddefined between the tube 300 and the small pipes 320. The supplementarysecond capillary wick 240 interconnects the first wick structures at theevaporating section and at the condensing section. The other structureof the heat pipe of the fourth embodiment is similar to that of thefirst embodiment.

The tube 300 and the pipes 320 in the preferred embodiments are made ofmetal sheet. Alternatively, they can be made of metal mesh. The tube 300and the pipes 320 are made of metal materials such as copper oraluminum. Alternatively they can be made of non-metal material such asplastics or resin. A cross-sectional area of the tube 300 or the pipes320 can also be square or rectangular, according to the shape of heatpipe.

It is believed that the present embodiments and their advantages will beunderstood from the foregoing description, and it will be apparent thatvarious changes may be made thereto without departing from the spiritand scope of the invention or sacrificing all of its materialadvantages, the examples hereinbefore described merely being preferredor exemplary embodiments of the invention.

1. A heat pipe comprising: a casing containing a working fluid therein;a capillary wick arranged inside of the casing and extending in an axialdirection of the casing; and a tube surrounding the capillary wick andan inner surface of the tube contacting with a surface of the capillarywick in the casing; wherein a vapor passage is formed between an outerwall of the tube and an inner wall of the casing and a liquid channel isdefined by the capillary wick, and wherein the vapor passage isseparated from the capillary wick by the tube, the working fluid invapor and liquid states respectively flowing along the vapor passage andthe liquid channel from one end towards an opposing end of the casing inopposite directions.
 2. The heat pipe as claimed in claim 1, wherein thecapillary wick comprises first capillary wicks provided in opposite endsof the casing and a second capillary wick interconnecting the firstcapillary wicks and extending in the axial direction of the casing, thetube surrounding the second capillary wick.
 3. The heat pipe as claimedin claim 2, wherein the capillary wick further comprises a thirdcapillary wick having a thinner thickness than that of the first andsecond capillary wicks, the third capillary wick extending from one ofthe first capillary wicks into the vapor passage and functioning toguide the working fluid in vapor into the vapor passage.
 4. The heatpipe as claimed in claim 1, wherein the casing comprises a rib disposedbetween the outer wall of the tube and the inner wall of the casing. 5.The heat pipe as claimed in claim 2, wherein the casing furthercomprises a plurality of spaced pipes surrounding the tube and asupplementary capillary wick is filled in each of the pipes andinterconnecting the first capillary wicks.
 6. The heat pipe as claimedin claim 5, wherein the vapor passage is enclosed by the casing anddefined between the tube and the pipes.
 7. The heat pipe as claimed inclaim 1, wherein the tube is made of metal.
 8. The heat pipe as claimedin claim 1, wherein the tube is made of one of plastics and resin.
 9. Aheat pipe comprising: a metal casing having an inner wall therein anddefining an evaporating section for receiving heat, a condensing sectionfor releasing the heat and an adiabatic section between the evaporatingand condensing sections; a working fluid received in the metal casingand evaporated into vapor in the evaporating section and condensed intoliquid in the condensing section; a capillary wick extending in an axialdirection of the casing from the evaporating section through theadiabatic section to the condensing section and having a middle portionspaced from the inner wall of the metal casing; a tube contacting with asurface of the middle portion of the capillary wick; and a vapor passageformed inside of the metal casing and between the metal casing and themiddle portion of the capillary wick and a liquid channel defined by thecapillary wick; wherein the vapor at the evaporating section flowstowards the condensing section of the casing along the vapor passage andthe liquid at the condensing section of the casing returns to theevaporating section along the liquid channel, the tube separating thevapor passage and the liquid at a place wherein the tube is located. 10.The heat pipe as claimed in claim 9, wherein the capillary wickcomprises first capillary wicks arranged in the evaporating andcondensing sections and a second capillary wick interconnecting thefirst capillary wicks and extending in the axial direction of thecasing, the inner surface the tube contacting with the surface of thesecond capillary wick.
 11. The heat pipe as claimed in claim 10, whereinthe vapor passage is formed between an outer wall of the tube and theinner wall of the casing and the liquid channel is defined by the secondcapillary wick.
 12. The heat pipe as claimed in claim 9, wherein themetal casing further comprises a rib arranged between an outer wall ofthe tube and the inner wall of the casing.
 13. The heat pipe as claimedin claim 9, wherein the metal casing further comprises a plurality ofspaced pipes surrounding the tube, a supplementary capillary beingfilled in each of the pipes and interconnecting the capillary wick atthe evaporating and condensing sections.
 14. The heat pipe as claimed inclaim 10, wherein the first capillary wick at the evaporating sectionhas a thickness gradually decreased along a direction from theevaporation section toward the adiabatic section, and the firstcapillary wick at the condensing section has a thickness graduallyincreased along a direction from the adiabatic section toward thecondensing section.
 15. The heat pipe as claimed in claim 14, furthercomprising a third capillary wick extending from the first capillarywick at the evaporating section into the vapor passage.